1. Field of the Invention
The present invention relates to anti-friction linear motion bearings and, more particularly, to linear motion bearing assemblies which facilitate ease of manufacture and installation while effecting optimization of contact angle with the rolling elements.
2. Description of the Related Art
Linear motion bearing assemblies are well known in the art and are used extensively in a wide variety of machines, machine tools, transfer systems and other equipment where machine elements move with respect to one another. These assemblies typically include a bearing carriage mounted for movement along a modified Y-beam, I-beam or T-beam shaped rail. Load bearing and return tracks are provided in association with the bearing carriage for a plurality of recirculating rolling elements such as, for example, balls or rollers. These rolling elements travel alternately through the load bearing tracks and return tracks to facilitate movement of the bearing carriage along the rail with minimum friction.
End caps are usually located on the ends of the bearing carriage and may have turnarounds formed therein for transferring the rolling elements from the load bearing tracks to the return tracks. The turnarounds typically comprise a semi-toroidal shaped track dimensioned and configured for the particular rolling element being employed. At the center of the semi-toroid, an internal guide may be provided to smooth the movement of the rolling elements in the turnarounds.
The return tracks typically take the form of bores or channels conforming in size to the dimensions of the rolling elements which are cut or drilled into the depending legs of the bearing carriage. See, for example, U.S. Pat. No. 4,932,067 to Pester et al. The overall structure of this type of linear motion bearing assembly typically requires the extensive use of expensive high quality bearing steel in order to yield a bearing of sufficient strength and longevity. This is at least partially necessitated by the fact that load bearing portions require the strength and rigidity of bearing steel and are usually monolithically formed directly in the structure of the bearing carriage and/or the rail. See, for example, U.S. Pat. No. 4,637,739 to Hattori. Fabrication of the rails and/or carriages from such material requires numerous precision machining steps as well as hardening processes on designated areas such as, for example, the contact portions of the load bearing tracks in both the carriage and the rail. This process is extremely costly and, depending on the bearing assembly structure, requires elaborate and expensive machining equipment. In addition, one characteristic of high quality bearing steel is its rigidity. This characteristic results in a requirement for extreme precision in grinding the load bearing tracks and highly accurate installation of the linear motion bearing assembly to avoid overly stressing the contact portions.
Attempts have been made in the past to isolate the highly stressed contact points within the linear motion bearing assemblies by providing inserts which are mounted to conventional rail or carriage structure. See, for example, U.S. Pat. Nos. 3,900,233 and 4,025,995 to Thomson. Load bearing track inserts are also shown in U.S. Pat. Nos. 4,515,413, 4,527,841, 4,531,788 and 4,576,421 to Teramachi and U.S. Pat. No. 4,576,420 to Lehmann et al. However, these linear motion bearings do not address or overcome the inherent rigidity problem characteristic of these materials. Thus, extreme precision and accurate placement are still very definite factors affecting the operation and longevity of the linear motion bearing assembly.
Attempts have also been made in the past to reduce this inherent rigidity of structures formed entirely of high quality bearing steel. For example, U.S. Pat. No. 5,217,308 to Schroeder discloses an internal carriage structure for a linear motion bearing assembly. The carriage is configured to be supported within a frame structure by four inward facing steel raceways mounted to the frame structure. The frame structure is constructed of aluminum and is configured to allow for flexure of the upper races to take up clearances within the assembly.
Therefore, it would be highly desirable to have an easily manufactured linear motion bearing assembly which reduces the need for extensive precision drilling, hardening and/or grinding of contacting surfaces on the carriage and on the rail while providing a dependable bearing assembly which is capable of a high degree of flexural movement when placed under load to optimize the contact angle of the rolling elements in the load bearing tracks.
Accordingly, it is one object of the present invention to provide an easily manufactured linear motion bearing assembly which minimizes the use of expensive high quality bearing steel while providing the capability of optimizing the contact angle of the rolling elements and load bearing tracks.
It is a further object of the present invention to provide a linear motion bearing wherein the contacting load bearing portions of the carriage and rail are formed of high quality steel inserts which are fitted into relatively flexible carrier structure.
It is also an object of the present invention to provide a reliable linear motion bearing assembly which can be easily fabricated with a minimum of bearing steel elements without the need for precision grinding and hardening directly on the carriage block and/or rail.
These and other highly desirable objects are accomplished by the present invention in a linear motion bearing having bearing steel track inserts fitted into the depending legs of the bearing carriage and the rail. The balance of the bearing assembly is constructed of more flexible material such as, for example, machine grade aluminum, plastics or less expensive grades of steel to facilitate easy and accurate assembly of the linear motion bearing assembly. The parts are configured without the need for precision grinding or hardening of tracks directly on the carriage and/or rail.
Objects and advantages of the invention are set forth in part herein and in part will be obvious therefrom, or may be learned by practice with the invention, which is realized and attained by means of the instrumentalities and combinations pointed out in the appended claims. The invention consists of novel parts, constructions, arrangements, combinations, steps and improvements herein shown and described.